JPS636622B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to manganese steel. High-strength steel, known as maraging steel, contains iron with nickel (approximately 18%) and molybdenum (approximately 5%).
%). These steels are believed to have toughness as well as strength. Heat treating these steels does not require rapid cooling, so large parts can be successfully treated and decarburization problems do not occur. The heat treatment required to make these steels high strength is known as "maraging" and is heated to 800℃ to 900℃.
First solution annealed at 450℃~500℃ then steel
This involves heating for several hours. The high strength achieved by this heat treatment is due to the alloying components contained in the steel, especially the content of nickel. Attempts to replace nickel with manganese in this type of steel are interesting because manganese has a similar effect to nickel when added to steel, and manganese is less expensive than nickel. Previous studies by the inventors and other experts have shown that steels based on various iron-manganese compositions containing additive elements such as molybdenum or silicon or titanium have improved strength by maraging-type heat treatment. I have confirmed that it is not possible. Unfortunately, as these steels become stronger, they also become very brittle, so this effect clearly limits their usefulness. One of the objects of the invention is to provide a high strength iron-manganese steel based on maraging type steels that combines high strength with acceptable toughness. At temperatures between 910°C and 1435°C, metallic iron has a crystal structure known as face-centered cubic (γ phase) and 910°C.
It can exist in two types of crystal structures: a body-centered cubic crystal structure at temperatures below 1435 °C (α phase) and a body-centered cubic crystal structure at temperatures between 1435 °C and the melting point (δ phase). When alloying elements are added to iron, the temperature range in which each of the above phases stably exists changes. For example, both nickel and manganese
Since it stabilizes the γ phase at temperatures below 910°C and above 1435°C, it is considered to be a γ phase stabilizing element.
If a sufficient amount of nickel or manganese is added, an alloy steel can be produced at room temperature with a crystal structure consisting partly or entirely of the gamma phase. Now, the maraging phenomenon depends in part on the transformation from a γ-phase structure to an α-phase structure steel at a temperature relatively close to room temperature (to be precise, the body-centered cubic phase formed near room temperature is Usually referred to as the α' phase, it is produced by a shearing mechanism rather than by the usual diffusion mechanism, and has a slightly body-centered tetragonal crystal structure, depending on the carbon content of the steel. (Hereinafter, all body-centered cubic phases will be referred to as α phases). Whatever elements (eg molybdenum) are added to the steel to harden it during the subsequent maraging at 450°C to 500°C, this transformation phenomenon results in supersaturation of the alpha phase. We believe that if the steel is not completely transformed into an α-phase structure, but retains some amount of the γ phase (or the ε phase, which is known to form as part of the transformation sequence in iron-manganese systems), It has been found that good toughness can also be maintained during maraging to increase strength. It is envisaged that the dispersion of these phases may take place in two ways. First of all, the gamma and epsilon phases (gamma/epsilon phases) do not increase in strength upon maraging, but they do form a set of crack arrest zones in the steel. Second, elements that are present at impurity levels in the steel and can promote the development of brittleness in the alpha phase are probably absorbed by the gamma/epsilon zone and rendered harmless. According to the invention, apart from impurities, manganese 11.0-13.5% by weight; molybdenum 2.0-6.59% by weight
and at least 1% by weight of tungsten
A manganese steel is provided with high strength and toughness comparable to maraging steels containing 0.002-0.2% by weight carbon and the balance iron. This invention also provides, apart from impurities, manganese 11.0-13.5% by weight; at least one of molybdenum 2.0-6.59% by weight and tungsten 2-10% by weight; carbon 0.002
The present invention provides a manganese steel having high strength and toughness comparable to maraging steel containing iron in an amount of up to 0.2% by weight, at least 0.2% by weight of at least one of aluminum, titanium, and Mitsushi metal, and the remainder. Furthermore, the present invention also provides a method for producing the manganese steel. That is, according to the present invention, apart from impurities, manganese 11.0 to 13.5% by weight; at least one of molybdenum 2.0 to 6.59% by weight and tungsten 2 to 10% by weight; carbon 0.002
To produce manganese steel with high strength and toughness comparable to maraging steels containing ~0.2% by weight and the balance iron, the steel is heated at temperatures between 800°C and 1100°C.
maraging steel, consisting of first solution annealing at a temperature in the range of 400 °C to 550 °C, followed by cooling to at least room temperature and maraging for a period of up to 100 hours at a temperature in the range of 400 °C to 550 °C. It also provides a method for manufacturing manganese steel with comparable high strength and toughness. For best results we suggest producing the steel by vacuum melting or air melting. A preferred heat treatment includes an initial solution treatment at a temperature of 800 DEG C. to 1100 DEG C. for a period of time depending on the size of the treatment member. The steel is then cooled from the solution temperature to at least room temperature. This cooling rate does not require close regulation.
The alpha and gamma phases may be separated by, for example, brief immersion in liquid nitrogen or cooling below zero by well-known and conventional techniques before the final maraging to increase strength. It may be necessary or desirable to establish a satisfactory ratio. Next maybe
400℃ to 550℃ for a period of up to 100 hours
Maraging is carried out at a temperature within the range of . The reason for limiting the action and content of manganese steel components according to this invention is as follows: Manganese is added to control the transformation of steel. By adjusting the manganese content within the above-mentioned range, steel with an optimum ratio of martensite to austenite can be produced. Molybdenum is added for two reasons. That is, it reduces the brittleness of martensite and promotes maraging when maraging properties are desired. Manganese is 11.0
Below 13.5% by weight, the amount of austenate remaining after solution treatment at the above-mentioned temperatures is insufficient to promote good toughness, and above 13.5% by weight, the amount of austenite remaining after solution treatment is too high. As a result, the steel no longer exhibits the necessary high strength. If molybdenum is less than 2% by weight, brittleness cannot be prevented, and if it exceeds 6.59% by weight, iron-molybdenum precipitates remain even after solution treatment, producing a hard and unstable steel. Tungsten can replace molybdenum as an age hardening component in the steel of the present invention.
Age hardening does not occur when tungsten is less than 2% by weight. Furthermore, the upper limit is 10% by weight due to cost and effectiveness of addition. The atomic weight of tungsten is approximately twice that of molybdenum, so assuming that age hardening by both occurs through the same type of hardening mechanism, approximately twice the weight of tungsten is required to obtain the same degree of age hardening. shall be. Carbon, like manganese, has a good effect on achieving the phase ratio between martensitic and austenitic phases. If the carbon content is greater than 0.2% by weight, the steel will have an excessively high proportion of austenite, which will have a negative effect on the mechanical properties of the steel. If it is less than 0.002% by weight, the effect of addition cannot be achieved. Silicon, sulfur and phosphorus are considered impurities in this invention steel, but silicon up to 0.4% by weight, sulfur up to 0.02% and phosphorus up to 0.03% by weight are allowed. If these impurities exceed the above-mentioned limit amounts, they will adversely affect the mechanical properties of the steel. Aluminum, titanium, and Mitsushi metal act as impurity scavengers and facilitate separation of impurities in the second phase. These components exhibit similar effects, and if these components are contained in an amount greater than 0.2% by weight, precipitates are formed at grain boundaries, leading to a decrease in the mechanical properties of the steel. Solution treatment temperature from 800℃
The reason for specifying 1100°C is that a temperature below 800°C is insufficient for all of the added molybdenum to be dissolved, resulting in a decrease in maraging response. Solution treatment at temperatures above 1100°C significantly increases the size of the parent austenite grains, resulting in a loss of mechanical properties. Also,
The reason why the maraging temperature was specified as 400℃ to 550℃ is that the maraging response is slow at temperatures below 400℃, and as a result, sufficient maraging cannot be performed within an industrially practical time. ,
At temperatures above 550°C, this maraging response is rapid, but the maraging effect is smaller than the magnitude of maraging at temperatures below 550°C. A suitable steel has the following composition (% by weight): Manganese 12.5% Molybdenum 4.0% Carbon 0.02% (maximum) Sulfur 0.02% (maximum) Silicon 0.02% (maximum) Phosphorus 0.01% (maximum) After vacuum melting, the steel is first solution treated at 900°C for 1 hour, air cooled, then quenched in liquid nitrogen before maraging at 450°C for 5 hours. The above heat treatment produces a steel with the following properties: 0.1% Proof strength 1150MN/ ^m2 Tensile strength 1450MN/ ^m2 Elongation (%) 30 Reduction of area (%) 70 Toughness (CVN)
85 Joule (hereinafter abbreviated as J) Hardness 430HV One of the advantages of this invention is that the second phase retained in the steel acts as an impurity scavenger, allowing greater tolerance in the selection of the purity of the iron source used. It is to do so. Therefore, lower grade starting materials can be used when this second phase is present. Also, higher concentrations of impurities can be tolerated.
It is possible to produce high-strength steel of acceptable quality by air melting, which is considerably easier and cheaper to process. As a result, the steels of this invention are less expensive than conventional steels of comparable strength and stiffness. Another factor contributing to the steel of this invention being a low cost product is the use of manganese instead of nickel. Syalpy V-notch (CV) of 100 joules or more
N.) A steel with a yield value of up to 800 MN/ ^m2 along with a notch toughness of impact value is obtained if the balance between carbon and manganese is defined by this invention with manganese at 11% to 12% by weight. , 0.02% carbon by weight
If maintained at ~0.12 wt.%, it can be produced without the need for maraging after solution treatment, which has clear energy advantages, is cost saving, and reduces molybdenum requirements. The amount is the same as or less than that required in the aging alloy composition. As mentioned above, steel containing manganese and molybdenum and retaining the second phase after solution treatment can obtain high strength by cold working to transform the retained second phase, γ phase. There are additional benefits. Different examples of the manganese steel and the heat treatment method thereof according to the present invention will be explained below. Example 1 Steel was made by vacuum melting pure materials, followed by solution treatment and then maraging: Composition (% by weight):

[Table] Alloy grade: Industrially pure (electrolytic iron base) Manufacturing method: Vacuum melting Heat treatment: Solution treatment at 900℃ for 1 hour, then maraging treatment at 450℃ for 5 hours Mechanical properties (room temperature):

[Table] Impact resistance (low temperature): CVN80 joule example at -70℃ 2 Steel made from pure materials by simply vacuum melting and then solution treatment: Composition (wt%):

【table】 Alloy grade: industrially pure (electrolytic iron base) Manufacturing method: Vacuum melting Heat treatment: Solution treatment at 900℃ for 1 hour Mechanical properties (room temperature):

[Table] Impact properties (low temperature): CVN 160 joules (J) at -70°C CVN 40 joules at -196°C Example 3 Materials graded as impure by air dissolving and then maraging after solution treatment Steel was made from: Alloy composition (wt%):

[Table] Alloy grade: Impure (mild steel base) Manufacturing method: Air melting Heat treatment: Solution treatment at 900℃ for 1 hour, then maraging treatment at 450℃ for 5 hours Mechanical properties (room temperature):

[Table] Impact resistance (low temperature) CVN 50 joules at -50°C CVN 40 joules at -100°C Example 4 Steel was made from industrially pure materials by air melting, solution treatment and then maraging. Alloy composition (wt%):

[Table] Alloy grade: Industrial pure (electrolytic iron base) Manufacturing method: Air melting Heat treatment: Solution treatment at 900℃ for 1 hour, then maraging treatment at 450℃ for 5 hours Mechanical properties (room temperature):

[Table] Impact resistance (low temperature): CVN 58 joules at -50°C CVN 32 joules at -100°C Example 5 Steel made from material graded as impure by solution treatment and then cold working: Alloy composition (wt%):

[Table] Alloy grade: Impure Manufacturing method: Vacuum melting Heat treatment: Solution treatment at 900℃ for 1 hour, 33%
Cold worked to achieve a drawing of Mechanical properties (room temperature):

[Table] Example 6 Steel was made from material graded as pure by vacuum melting, then solution treatment and cold working: Alloy composition (% by weight):

[Table] Alloy grade: Industrially pure Manufacturing method: Vacuum melting Heat treatment: Solution treatment at 1000℃ for 1 hour, then cold working to 45% reduction Mechanical properties (room temperature):

[Table] In the above examples, and during manufacture, after vacuum or air melting, the steel of each example was reduced by hot working by reducing it by more than 70% of its original cross-sectional area. The advantageous properties of cast steel made in accordance with this invention are typically, but not always, achieved by hot treating the steel prior to solution treatment. In particular it depends on moderately fine grain size. However, although the properties obtained in the as-cast or hot-treated condition can be compared favorably with other steels in that condition, in order to optimize the properties of cast steel, it is necessary to 2-3 at a temperature of 1250℃
Time homogenization annealing is recommended. Example 7 A maraging steel with the following composition was produced by vacuum melting, solution treatment, and then maraging: Alloy composition (wt%):

[Table] Manufacturing method: Vacuum melting + high temperature processing Heat treatment: Solution treatment at 900℃ for 1 hour, then maraging at 500℃ for 40 hours Mechanical properties: Hardness (before maraging treatment) HV ₃₀ 335 Hardness (maraging treatment) After) HV ₃₀ 411 Toughness [Sharp V-Notch (CVN) units (J)] Before maraging 172 After maraging 80 Example 8 This example illustrates the effect of aluminum and titanium. An alloy with the following components was prepared by vacuum melting. Alloy A is the base alloy for comparison with Alloy B and Alloy C, which contain effective amounts of aluminum and titanium.

[Table] Toughness After initial maraging at 450°C for 5 hours (CVN J) Alloy A 66 54 Alloy B 73 56 Alloy C 79 68 (Note: CVN is an abbreviation for Sharpie V-Notch.
The effect of aluminum and titanium is probably due to heat refining. Mitsushi Metal has a similar effect.

Claims (1)

[Claims] 1. Apart from impurities, 11.0 to 13.5% by weight of manganese; at least one of 2.0 to 6.59% by weight of molybdenum and 2 to 10% by weight of tungsten; 0.002% of carbon
Manganese steel with high strength and toughness comparable to maraging steels containing ~0.2% by weight and iron as the balance. 2. It has high strength and toughness comparable to the maraging steel according to claim 1, which contains, apart from impurities, 12.5% by weight of manganese, 4.0% by weight of molybdenum, 0.002 to 0.02% by weight of carbon, and the balance iron. Manganese steel. 3 Apart from impurities, manganese 11.0-13.5% by weight; at least one of molybdenum 2.0-6.59% by weight and tungsten 2-10% by weight; carbon 0.002
~0.2% by weight; Manganese steel with high strength and toughness comparable to maraging steel containing iron with at least 0.2% by weight of at least one of aluminum, titanium, and Mitsushi metal and the remainder. 4 Apart from impurities, manganese 11.0-13.5% by weight; at least one of molybdenum 2.0-6.59% by weight and tungsten 2-10% by weight; carbon 0.002
To produce manganese steel with high strength and toughness comparable to maraging steels containing ~0.2% by weight and the balance iron, the steel is heated at temperatures between 800°C and 1100°C.
maraging steel, consisting of first solution annealing at a temperature in the range of 400 °C to 550 °C, followed by cooling to at least room temperature and maraging for a period of up to 100 hours at a temperature in the range of 400 °C to 550 °C. A manufacturing method for manganese steel with comparable high strength and toughness. 5. A method for producing manganese steel having high strength and toughness comparable to the maraging steel according to claim 4, wherein the first solution treatment is carried out at 900° C. for 1 hour. 6. A method for producing manganese steel having high strength and toughness comparable to maraging steel according to claim 4, wherein the steel is cooled to a temperature below zero degrees before maraging.